Yellow to red pigment



Patented Sept. 12, 1933 I YELLOW TO BED PIGMENT Ekbert Lederle,

and Hans Ludwigshaten-on-thc-Rhinc, Georg Grimm, Heidelberg, Germany,

assignors to I. G. Farbenindustrie Aktiengesellschai't, Frankfurt-on-the-Main, Germany No Drawing. Application August 10, 1931, Serial No. 556,310, and in Germany August 14, 1930 8 Claims. (Cl. 134-87) The present invention relates to yellow to red pigments and process of producing same.

We have found that mixed crystals from lead molybdate or lead tungstate and lead chromate are especially suitable as yellow pigments by reason of their high covering power and color strength. For example mixed crystals of the composition: 95 per cent of PbCrOr and 5 per cent PbWO4 have a covering power amounting to more than double that of pure lead chromate. The covering power is not appreciably diminished when a part of the lead is replaced by the cheaper barium or strontium, thereby partly equalizing the extra cost of the product due to the content of tungstic or molybdic acid. Similarly, lead sulphate may be introduced as a further component in the mixed crystals whereby surprisingly the color of the mixed crystals is changed towards scarlet red and the color strength and the covering power are substantially improved. The preparation may be efiected by intimately mixing the components in the moist state and allowing them to recrystallize. The mixed crystals are preferably prepared, however, by precipitating the components from a common solution. The components probably first precipitate separately but rapidly combine to form mixed crystals by reason of their intimate admixture. This process may be clearly followed by the change in the color of the precipitate. Thus for example, a pigment having the composition, 75 per cent of PbCroi, 20 per cent of PbSOi and 5 per cent of PbM0O4 is first precipitated as a lemon yellow precipitate but changes in the course of half an hour to a brilliant scarlet red color. The formation of the mixed crystals may even be effected by the conversion of lead compounds diflicultly soluble in water with a solution which contains the necessary anions, as for example by treating lead compounds which are insoluble or diflicultly soluble in water with an aqueous solution of chromates and tungstates and/or molybdates.

In addition to the absence of lead oxide, the said red and orange colored products have the special advantage of an excellent strength. Thus, the scarlet red pigment already mentioned has a covering power about ten times as great as the usual chrome red having the composition PbO.PbCrO4.

Particularly valuable are the pigments containing between 40 and 95 per cent of lead chromate, between 2 and lead molybdate, the rest being lead tungstate or lead sulphate, in view of their color strength and fastness to light of these pigments.

As already mentioned the lead may partially be replaced by barium or strontium. Up to 80 per cent of the lead may thus be replaced whereby the fastness of the pigments against alkalies 'is increased, but it should be kept in mind that go by such replacement the color strength is diminished. Pigments showing a good fastness against weak alkalies which at the same time have good other tinctorial properties, are those in which up to 40 per cent of the lead is replaced by barium or strontium.

The following examples will further illustrate the nature of this invention but the invention is not restricted to these examples.

Example 1 For the preparation of a mixed crystal pigment containing 97.5 per cent of PbCrOr and 2.5 per cent of PbMoOi.

100 kilograms of lead nitrate are dissolved in 1.5 cubic meters of water and the pigment is precipitated by the addition of a solution of 56.7 kilograms of potassium chromate and 1.5 kilograms of ammonium molybdate in 1.5 cubic meters of water. A reddish yellow pigment having excellent color strength and great covering power is obtained;

Example 2 Example 3 For the preparation 01 a mixed crystal pigment containing 55 per cent of PbCrOr, 40 per cent of BaCrOr and 5 per cent of PbMoOi corresponding to the formula:

9.8 kilograms of barium chloride are added to a solution of 20 kilograms of lead nitrate in 500 liters of water whereby a part of the lead is precipitated as lead chloride. A solution of 18.4 kilograms of potassium chromateand 1 kilogram of ammonium molybdate in 500 liters of water is' Example 4 For the preparation of a pigment consisting of mixed crystals of the composition:

Pb (CroxwSazMoaos) 04.

Three solutions of 25, 6.7 and 1.7 kilograms of lead nitrate in 300, 150 and 50 liters of water respectively are prepared. By the addition of solutions of 14.6 kilograms of potassium chromate, 2.9 kilograms of anhydrous sodium sulphate and 1 kilogram of ammonium molybdate in 300, 150 and 50 liters of water respectively, 24.2 kilograms of yellow PbCrO4, 6.0 kilograms of white PbS04 and 1.8 kilograms oi. white PbMoO4 are precipitated. The three precipitates are combined while intimately mixing them and after some time a scarlet red pigment is obtained which is filtered, washed and dried at 100 C.

Example 5 For the preparation of a pigment consisting of mixed crystals of the composition:

Example 6 For the preparation of a pigment consisting of mixed crystals of the composition:

Pb (CIomsSoaooMOaozs) 04.

The pigment is precipitated from a solution of 100 kilograms of lead nitrate in 1.5 cubic meters of water by the addition of a solution of 47.7 kilograms of potassium chromate, 1.5 ln'lograms of ammonium molybdate and 8.7 kilograms of an-.

hydrous sodium sulphate: in 1.5 cubic meters of water. The original pale yellow precipitate becomes somewhat darker when allowed to'stand. The pigment is flltered'ofi well washed and dried at about 100 C.

Example 7 For the preparation of a pigment consisting of mixed crystals of the composition:

Pbo.aSro.2(CraasSasMOaM) O4.

5.3 kilograms of crystalline strontium chloride are added to a solution of 26.7 kilograms of lead nitrate in 500 liters of water, whereby a part of the lead is precipitated as lead chloride. A solution of 5.8 kilograms of potassium chromate, 8.7 kilograms of anhydrous sodium sulphate and 1 kilogram of ammonium molybdate in 500 liters of water is added to the well stirred suspension. After about half an hour the precipitate has assumed a Vermilion red color. It is washed, filtered and dried at about 100 C.

which when worked up in the usual manner forms Example 8 I For the preparation of a red pigment consisting of mixed crystals of the composition:

' 38.3 kilograms of lead acetate are dissolved in 50 liters of water and a solution of 1.96 kilograms of ammonium molybdate, 13.6 kilograms of potassium chromate and 2.8 kilograms of anhydrous sodium sulphate in 50 liters of water is slowly added at ordinary temperature while stirring. First a brilliant yellow precipitate is formed which changes in the course of 1 hours to Vermilion.

Example 9 For the preparation of an orange red pigment consisting of mixed crystals of the composition: Pb (C1'0.4M00.6) O4.

A solution of 11.6 kilograms of ammonium molybdate and 7.8 kilograms of potassium chromate in 50 liters of water is added to a solution of 33.3 kilograms of lead nitrate in 50 liters of water. An orange red precipitate is obtained a. pigment of great color strength.

Example 10 A warm solution of 77.5 kilograms of potassium chromate, 10.5 kilograms of anhydrous sodium sulphate and 4.5 kilograms of ammonium molybdate in 5000 liters of water is added to a solution of 154 kilograms of lead nitrate and 13.5 kilograms of barium nitrate in 5000 liters of water warmed to between 40 and 50 C. The precipitate formed is worked up as usual and yields an orange pigment having the composition: Pbo.9Bao.1(Cro.aSo.15MOo.o5) 04.

Example 11 A solution of 50 kilograms of potassium bichromate, 17.5 kilograms of potassium sulphate and 9.8 kilograms of ammonium molybdate in 5000 liters of water is slowly added, while stirring, to a solution of 166.5 kilograms of lead nitrate in 5000 liters of water. The pale yellow precipitate first formed is converted, while completing precipitation, into a clear red precipitate with a bluish tinge. The excess of acid is neutralized, the precipitate filtered oil and dried at about 100 C. The pigment thus obtained has a very good covering power and corresponds to the formula: Pb(C1o.'1S0.2M0o.1)O4.

What we claim is:

1. As anew article of manufacture mixed crystals suitable as yellow to red pigment coloring matters comprising lead chromate and at least one salt of lead with an acid selected from the group consisting of molybdic and tungstic acid.

2. As a new article of manufacture mixed crystals suitable as yellow to red pigment coloring matters consisting of from 40 to 95 per cent of lead chromate, from 2 to 15 per cent of lead molybdate, the rest being a salt of lead and an acid selected from the group consisting of tung- 40 stic and sulphuric acid.

3. As a new article of manufacture mixed crystals suitable as yellow to red pigment coloring matters containing lead chromate and at least one salt of lead with an acid selected from the group consisting of molybdic and tungstic acid and containing furthermore lead sulphate incorporated in their crystal structure.

4. As a new article of manufacture mixed crystals as claimed in claim 1 containing in addition 15C use? to lead a salt selected from the group consisting of-barium chromate, strontium chromate, barium sulphate, strontium sulphate, barium molybdate and strontium molybdate.

5. As a new article of manufacture mixed crystals suitable as yellow to red pigment coloring matters containing lead chromate and at least one salt of lead with an acid selected from the group consisting of molybdic and tungstic acid, containing lead sulphate incorporated in their crystal structure and containing in addition to the said lead salts a salt selected from the group consisting of barium chromate, strontium chromate, barium sulphate, strontium sulphate, barium molybdate and strontium molybdate.

6. As a new article of manufacture mixed crystals suitable as red pigment coloring matter having about the following composition: 70 molecular per cent of M04, 20 molecular per cent 0! PbSOl and 10 molecular per cent of PbM0O4.

'1. As a new article of manufacture mixed crystals suitable as red pigment coloring matter having about the following composition: molecular per cent of PbCrOk. 5 molecular per cent of PbSO4, 5 molecular per cent of PbMOOl, 10 molecular per cent of 30.804.

8. As a new article of manufacture mixed crystals suitable as yellow pigment coloring matter having about the following composition: 55 molecular per cent of PbCl'Oi. 40 molecular per cent of BaCrO4 and 5 molecular per cent of PbM0O4.

EKBERT LEDERLE. HANS GEORG 01mm. 

